The present invention relates to a fabric feed device of a sewing machine.
Generally, a conventional fabric feed device is subtantially composed of a feed dog for transporting a fabric to be sewn, a first cam for moving the feed dog up and down, a second cam for swingably moving a fork which is operatively connected to the feed dog through a rocking shaft for moving the feed dog in a horiziontal plane, and a feed regulator operatively connected to the fork to regulate the swinging movement of the fork. Thereby, the rocking movement of the rocking shaft to adjusts the movement amount of the feed dog in the horizontal plane. Thus, the feed dog is moved in a trapezoidal path, that is, horizontally moved while it is moved up and down, thereby to transport the fabric with respect to a needle.
According to the conventional device as mentioned above, if the fabric feed device is adjusted to feed (or transport) the fabric in a smaller amount in reference to the maximum forward amount C-max as shown in FIG. 11, the moving locus of the feed dog is reduced as indicated by a reference character C in which the moving amounts of the feed dog at the raised position 1.0 thereof are substantially equal on both sides of a center D.sub.0 of the total horizontal movement, provided that the level 0 is a needle plate, below which the feed dog will not transport the fabric. Namely, the initial position of the feed dog for transporting the fabric is shifted away from the machine operator compared with the maximum forward feeding locus C-max.
Therefore, with a sewing machine provided with such a type of fabric feed device, the machine operator is generally required to forwardly push the front edge of the fabric deep between the feed dog and the presser foot. This is especially the case when the fabric is sewn with straight stitches of smaller pitches, such as 1.5 to 2 mm or 5 mm, which are so frequently selected.
Further, in combination with this type of the fabric feed device, a stepping motor is often employed to adjust the inclination of the feed regulator, thereby to adjust the feeding amount (or pitch) of the fabric. In this case, the maximum feeding amount may be generally obtained by dividing the feeding amount into 30 steps or less of the stepping motor in consideration of the step angle and control period of the step motor, so as to properly adjust the moderate or medium feeding amounts of the fabric. Such a way of division will be sufficient for controlling comparatively large amount of the fabric feed. It is not, however, sufficient for controlling a smaller amount (pitch) of the fabric fed, for example, in case of button hole stitches, satin stitches requiring the feeding amount 0.3 to 0.5 mm.